Powerboat rooster tail depressor

ABSTRACT

A powerboat with a rooster tail depressor (RTD) includes a hull, a propulsion subassembly on the hull, and a rooster-tail-suppressing subassembly on the hull. The propulsion subassembly propels the hull forwardly, producing a propulsion discharge that extends rearwardly of the stern. The rooster-tail-suppressing subassembly extends rearwardly of the stern over at least a portion of the propulsion discharge where it functions to suppress the formation of a powerboat rooster tail (e.g., for radar signature reduction and increased propulsion efficiency). Various embodiments include one or more of (i) a canopy having a downwardly facing surface that is arched (either curved or faceted), (ii) lift-to-drag ratio enhancing steps in the downwardly facing surface of the canopy, (iii) a rooster-tail-suppressing subassembly configured to enable articulation of the canopy in yaw and in trim, (iv) a skeg for enhancing maneuverability of the boat hull, and (v) a conveniently removable and/or retractable rooster-tail-suppressing subassembly.

BACKGROUND OF THE INVENTION

1. Technical Field

This invention relates generally to the field of powered watercraft, andmore particularly to powerboats, seagoing vessels, and the like thattend to produce a rooster tail when moving forwardly.

2. Description of Related Art

When the hull of a powerboat is driven forward, whether by propellers,water jets, or some other propulsion subassembly on the vessel, thepropulsion subassembly often produces what can be called a propulsiondischarge. As the hull is propelled forwardly, the propulsion discharge(i.e., water) is forced into the air rearward of the powerboat's stern.The resulting plume of water behind the powerboat is commonly referredto as a “rooster tail” because it reminds one of the tail of a rooster.Such a rooster tail increases in size with vessel speed and can becomequite large.

One problem with powerboat rooster tails is that they can exposemilitary vessels to the enemy. The rooster tail can create a seriousradar signature that is useable by enemy fire control for acquiring,tracking, and attacking a vessel. Another problem relates to powerboatefficiency in that a large amount of energy is expended in creating therooster tail. Thus, powerboat manufacturers and users need a way toalleviate the above drawbacks.

SUMMARY OF THE INVENTION

It is a primary object of the present invention to alleviate theforegoing concerns. The present invention does so by providing what maybe called a “rooster tail depressor” (RTD). It is arooster-tail-suppressing assembly on the hull that takes the form of astructure (e.g., a canopy) extending rearwardly of the stern and overthe powerboat's rooster-tail-producing propulsion discharge. The RTDsuppresses the propulsion discharge and thereby the rooster tail in away that reduces the rooster tail radar signature while increasingpowerboat efficiency.

To paraphrase some of the more precise language appearing in the claimsand further introduce the nomenclature used, a powerboat constructedaccording to the invention includes a hull having a stern, a propulsionsubassembly, and a rooster-tail-suppressing structure on the hull. Thepropulsion subassembly functions as means for propelling the hullforwardly, producing a propulsion discharge at the stern as it does so.The rooster-tail-suppressing subassembly (i.e., the RTD) includes astructure on the hull that extends rearwardly of the stern and over atleast a portion of the propulsion discharge, where it functions as meansfor suppressing the formation by the propulsion discharge of thepowerboat rooster tail.

The RTD recaptures a large amount of energy in the rooster tail that isotherwise lost. Recapturing this energy produces a significant gain invessel lift, thereby reducing friction drag for a planing craft with anincrease in propulsion efficiency. The RTD traps the vertical componentof the propulsion discharge for vessel lift, while merely redirectingthe horizontal component downward without braking the vessel and therebyreducing its forward velocity.

In one preferred embodiment of the invention, therooster-tail-suppressing subassembly includes a canopy having adownwardly directed surface extending over at least a portion of thepropulsion discharge. The downwardly facing surface is arched (laterallyand/or longitudinally) and it may be faceted and/or curved. Anotheraspect of the invention concerns a means for enhancing lift-to-dragratio, including steps in the downwardly facing surface of the canopy.Another aspect concerns articulation of the rooster-tail-suppressingsubassembly in yaw and/or in trim. Still another aspect concerns a skegconnected to the rooster-tail-suppressing subassembly that functions asmeans for enhancing maneuverability of the boat hull. Yet another aspectconcerns a rooster-tail-suppressing subassembly that can be removed fromthe transom or folded back into the hull to reduce overall length of thepowerboat for storage or transport.

The invention, in all its forms, provides a powerboat with arooster-tail-suppressing RTD that significantly reduces powerboat radarsignature while improving powerboat efficiency. The followingillustrative drawings and detailed description make the foregoing andother objects, features, and advantages of the invention more apparent.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 of the drawings is a pictorial view of a powerboat constructedaccording to the prior art that is shown being propelled forwardly as itproduces a rooster tail extending rearwardly, with an X-Y-Z Cartesiancoordinate system included for spatial reference purposes;

FIG. 2 of the drawings is a diagrammatic plan view of a powerboat havinga first embodiment of a rooster-tail-depressing RTD constructedaccording to the invention, as viewed from overhead looking downwardlyalong a line of sight perpendicular to the X-Z plane of the Cartesiancoordinate system;

FIG. 3 of the drawings is a diagrammatic cross sectional view of thepowerboat and the first RTD embodiment as viewed in a vertical planecontaining a longitudinally extending line 3-3 in FIG. 2 that isperpendicular to the X-Y plane of the Cartesian coordinate system;

FIG. 4 a of the drawings is a diagrammatic cross sectional view of afaceted second RTD embodiment as viewed in a vertical plane containing atransversely extending line 4-4 in FIG. 2 that is perpendicular to theY-Z plane of the Cartesian coordinate system;

FIG. 4 b of the drawings is a diagrammatic cross sectional view of acurved third RTD embodiment as viewed in a vertical plane containing thetransversely extending line 4-4 in FIG. 2;

FIG. 5 is a diagrammatic elevation view (similar to FIG. 3) of a fourthRTD embodiment that includes lift-to-drag ratio enhancement steps;

FIG. 6 is a diagrammatic elevation view of a fifth RTD embodiment thatincludes a thrust deflector on the transom of the vessel (i.e., atransom thrust deflector or TTD);

FIG. 7 is a diagrammatic plan view of a sixth RTD embodiment that can bearticulated in yaw, about a pivotal axis that is perpendicular to theX-Z plane;

FIG. 8 is a diagrammatic elevation view of a seventh RTD embodiment thatcan be articulated in trim, about a pivotal axis that is perpendicularto the Y-Z plane; and

FIG. 9 is a diagrammatic elevation view of an eighth RTD embodiment thatincludes a skeg to enhance maneuverability and/or tracking.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 of the drawings shows a powerboat 10 constructed according to theprior art. The illustrated prior art powerboat 10 takes the form of amilitary vessel having a M-shaped hull 11 with a stern 12. As apropulsion assembly onboard the hull 11 (not shown) propels the hull 11forwardly, the propulsion discharge it produces (i.e., water) forms arooster tail 13. The rooster tail 13 has a radar signature that an enemycan detect. In addition, production of the rooster tail 13 consumesenergy and thereby decreases vessel efficiency.

FIG. 2 of the drawings is a diagrammatic plan view of a powerboat 20constructed according to the present invention. The powerboat 20includes a hull 21 having a stern 22 with a transom 23. The powerboat 20also includes a propulsion subassembly on the hull 21 that produces apropulsion discharge. The propulsion subassembly is not fullyillustrated, but it may include known types and kinds of propellersand/or jets that are centered on a longitudinally extending hull axis 24of the powerboat 20 extending parallel to the Z axis as shown in FIGS. 2and 3. The propulsion subassembly is depicted diagrammatically by apropeller 25 in FIG. 2. Various propeller positions relative to thetransom 23 are shown, including a water-jet propeller position furthestrearwardly of the transom 23 (i.e., toward the right margin of thedrawing sheet on which FIG. 2 appears, in the direction indicated by anarrow on the Z axis of the Cartesian coordinate system).

The propulsion subassembly functions as means for propelling the hull 21forwardly. In operation, the propeller 25 produces a rearwardly directedpropulsion discharge (i.e., water) that propels the hull 11 forwardly(in a direction opposite the direction indicated by the arrow of the Zaxis). The propulsion discharge is depicted diagrammatically in FIG. 1by two rearwardly directed arrows near the propeller 25; it tends toform a rooster tail extending upwardly and rearwardly from the stern 22,as mentioned above with reference to FIG. 1 and as depicteddiagrammatically in FIG. 3 by a broken line 26 shown extending upwardlyand rearwardly from the propeller 25.

According to the major aspect of the invention, the powerboat 20 has arooster tail depressor (i.e., an RTD) in the form of arooster-tail-depressing subassembly extending rearwardly of the stern22. The RTD functions as means for suppressing the formation by thepropulsion discharge of the powerboat rooster tail (the broken line 26in FIG. 3). A first RTD embodiment shown diagrammatically in FIGS. 2 and3 includes a canopy 27 that extends rearwardly of the stern and over atleast a portion of the propulsion discharge. The canopy 27 includes adownwardly facing surface 28 that deflects the propulsion discharge(i.e., the source of the rooster tail) downwardly as depicteddiagrammatically by the two redirected arrows beneath the surface 28 inFIG. 3. The width of the canopy 27 parallel to the X axis, the lengthparallel to the Z axis, and the outline are all functions of the vesselsize and speed in addition to being a function of propeller size,location, and function.

FIG. 4 a is a diagrammatic elevation view of a canopy 32 on a secondembodiment of the invention. The canopy 32 is faceted in the sense thatit includes a downwardly facing surface 32A having a cross sectionalshape in a vertical transverse plane parallel to the X-Y axis that isnot continuously curved; it includes multiple line segments or chordsinstead.

FIG. 4 b is a diagrammatic elevation view of a canopy 33 on a thirdembodiment of the invention. The canopy 33 is curved in the sense thatit includes a downwardly facing surface 33A having a cross sectionalshape in a vertical transverse plane parallel to the X-Y axis that iscontinuously curved. The shapes of the canopy 32 and the canopy 33 arefunctions of the propeller size, number, and location. Otherconsiderations affecting their shapes include construction material andattachment design.

FIG. 5 is a diagrammatic elevation view of a fourth embodiment of theinvention having a canopy 34 with a downwardly facing surface 34A thatincludes lift-to-drag ratio enhancement steps. The steps are designed topromote separation of the redirected rooster tail from the RTD as soonas possible. That is done to reduce wetted surface area and viscousdrag. The steps also convert any forward motion of the propeller wakeinto thrust.

FIG. 6 is a diagrammatic elevation view of a fifth embodiment of theinvention having a canopy 35 and an optional transom thrust deflector35A (TTD) on the transom 23 of the hull 21.

FIG. 7 is a diagrammatic plan view of a sixth embodiment of theinvention having a canopy 36 that is configured to be articulated in yaw(about a vertical pivotal axis that is perpendicular to the X-Z plane)as depicted by an arrow 36A. The canopy 36 can be articulated in yaw tocontrol the direction of the rooster tail, enhance control of thevessel, and/or pivot with the propeller in the case of a propeller thatarticulates is yaw for steering.

FIG. 8 is a diagrammatic elevation view of a seventh embodiment of theinvention having a canopy 37 that is configured to be articulated intrim (about a horizontal pivotal axis that is perpendicular to the Z-Yplane) as depicted by arrows 37A and 37B. The canopy 37 can bearticulated in trim to control the amount of lift generated by capturing(i.e., depressing) the rooster tail and/or to articulate in trim withthe propeller.

FIG. 9 is a diagrammatic elevation view of an eighth embodiment of theinvention having a canopy 38 with a downwardly depending skeg 38A (or“rather”) attached. The skeg 38A (or “rather”) enhances maneuverabilityof the vessel and/or improves tracking.

Thus, the invention provides a powerboat having arooster-tail-suppressing assembly that significantly reduces powerboatradar signature while improving powerboat efficiency. Various enhancedversions provide the additional benefits described. Although exemplaryembodiments have been shown and described, one of ordinary skill in theart may make many changes, modifications, and substitutions withoutnecessarily departing from the spirit and scope of the invention. As forthe specific terminology used to describe the exemplary embodiments, itis not intended to limit the invention; each specific term is intendedto include all technical equivalents that operate in a similar manner toaccomplish a similar purpose or function, it being intended, forexample, that the term “powerboat” includes any of various poweredwatercraft and seagoing vessels.

What is claimed is:
 1. A powerboat comprising: a hull having a stern; apropulsion subassembly on the hull that functions as means forpropelling the hull forwardly, said propulsion subassembly producing apropulsion discharge that extends rearwardly of the stern when the hullis propelled forwardly by the propulsion subassembly; and means forsuppressing the formation by said propulsion discharge of a powerboatrooster tail, including a rooster-tail-suppressing subassembly on theboat hull that extends rearwardly of the stern and over at least aportion of the propulsion discharge.
 2. A powerboat as recited in claim1, wherein the rooster-tail-suppressing subassembly includes a canopyhaving a downwardly facing surface extending over at least a portion ofsaid propulsion discharge.
 3. A powerboat as recited in claim 2, whereinthe downwardly facing surface of the canopy is arched.
 4. A powerboat asrecited in claim 2, wherein the downwardly facing surface of the canopyis faceted.
 5. A powerboat as recited in claim 2, wherein the downwardlyfacing surface of the canopy is curved.
 6. A powerboat as recited inclaim 2, wherein the downwardly facing surface of the canopy is archedlaterally and longitudinally.
 7. A powerboat as recited in claim 2,wherein the rooster-tail-suppressing subassembly includes means forenhancing lift-to-drag ratio, including steps in the downwardly facingsurface of the canopy.
 8. A powerboat as recited in claim 2, wherein therooster-tail-suppressing subassembly is configured to enablearticulation of the canopy in yaw.
 9. A powerboat as recited in claim 2,wherein the rooster-tail-suppressing subassembly is configured to enablearticulation of the canopy in trim.
 10. A powerboat as recited in claim2, wherein the rooster-tail-suppressing subassembly includes means forenhancing maneuverability of the boat hull, including an attached skeg.